The invention relates to setting up a connection between two wireless low-power devices. When two devices want to connect to each other some kind of notification of the need for connection must be made. Devices may signal their need all the time or every now and then. Compromises must be made to save batteries power, especially in small, simple devices meant for goods for sale. For example a CD-disc might have a small electronic chip in its cover and when a customer wants to know more about the CD he would get a URL to his Bluetooth device from the chip.
This problem can be solved by a system where all devices send advertising signals periodically and they listen on the same frequency for a while for reply (time driven). In this case the device, which sends the reply message, communicates the need for connection. This beacon like solution has the disadvantage that independent from the actual use, the operation time is limited by the battery power and the average power consumption for operation of the beacon.
The power consumption is the critical element of battery powered devices that use a short range radio link. The connection setup requires that the low power radio module is either advertising itself or listening periodically other advertising devices. For this reason, the radio system needs to be activated periodically, typically with a duty cycle below 1%. Thus, the device is using some power in trying to setup a connection even if there are no other devices in the vicinity and the lifetime of the battery becomes a limiting factor.
Wireless communication between two battery driven (non-plugged) devices places special criteria to device discovery (idle mode operation from the radio perspective) since usually neither device can be continuously active. Hence, a trade off between connection setup, power efficiency and range is inevitable. In Bluetooth (BT) this trade-off is solved by compromising the connection set-up delay and as well as the idle mode duty cycle. See BT baseband specification.
In this scheme all devices send a device advertising message in a predefined frequency after which they listen in the same frequency for possible responses for a short period of time. In other words, the radio parts of the low power device will be activated in a time driven fashion, where the activation interval is application driven and it is based on the connection set-up delay and power efficiency needs of the device. Whereas the response to a time driven advertising message is event driven, i.e. the responding device has a need to establish a connection with the advertising device.
A natural enhancement to the discovery scheme would be that the device having the need to establish the connection sends a wake up message in order to avoid unnecessary periodical advertisement, which consumes power. A method to achieve this is that the sleeping device turns regularly only on its RF front end LNA (low noise amplifier) and a RSSI (relative signal strength indicator) measurement unit, (i.e. has a transponder) to detect whether received energy level exceeds a threshold, which will then be considered as a wake-up message. Compared to periodical advertisement which requires ramp up for whole transmission and receiving chains this is clearly more power efficient. Unfortunately, if only RF front end and LNA were activated all energy inside the band filter would be included in the RSSI measurement and e.g. in the 2.4 GHz ISM a microwave oven could turn the device active continuously, i.e., the power efficiency gain is lost.
The following basic technologies are provided:                a transponder architecture (see FIG. 2),        a transponder using RF field energy for wireless sensors (see FIG. 3), and the technical implementation of the suitable power detector for the concept (see FIG. 4).        
A connection set up protocol, which includes predefined channels for devices or people to broadcast their presence is known a priori.
An improvement would be that the device which wants to establish a connection would make the initiative step. Now the sleeping device to which the connection is intended listens for the wake-up signals with a transponder or other suitable sensor (event driven). So there is no need for periodical advertising signals and power can be saved. Similar solutions are known in naval navigation as “racon” systems.
One problem is that the transponder (or other sensor) may activate from any energy on the frequency band such as other Bluetooth—/WLAN—(Wireless Local Area Network)/ISM—(Industrial, Scientific, and Medical Frequency band at 2.4 GHz) devices, microwave ovens etc.
The first time driven system will work well in areas with an increased radio level such as towns with a lot of radio frequency emitting devices such as baby-phones, low power walkie-talkies, radio controlled central-locking for cars and the like.
The second event driven system will work well in areas with a reduced radio level such as countrysides with nearly no radio frequency emitting devices.
The state of the art does not provide a solution that can be applied in urban as well as in the country i.e. in highly and lowly radio frequency polluted areas.
All the above approaches for a wake up and communication setup are not suitable for the use environments in which the ISM band activity is not known. Therefore, a wake up and communication setup method and device architecture is needed which is capable to overcome these problems.